It is proposed to continue our kinetic and mechanistic studies pertaining to hydration-dehydration reactions with particular emphasis on erythrocyte carbonic anhydrases (carbonate hydrolyases EC4.2.1.1). Our earlier work has appeared in Biochemistry, J. Amer. Chem. Soc., J. Phys. Chem., J. Org. Chem., and Science. Our proposed work also exploits the remarkable versatility of carbonic anhydrases from red blood cells both with respect to hydration and hydrolysis. Work in progress uses Zn(II)-, Co(II)-, Mn(II)-, Cd(II)-, and Ni(II)-carbonic anhydrases and exploits temperature jump, stopped-flow, NMR, ORD/CD and O18-exchange techniques over a wide range of pH. We are studying the elementary enzymic steps and their combination in the overall mechanism of hydration-dehydration in both H2O and D2O. Other developments concern: (a) studies of model systems for rate acceleration and specificity; (b) comparative studies of apo- and native enzyme; (c) partial denaturation and reactivation; (d) sulfonamide inhibition; (e) active site modification; (f) enzyme interaction with proteins and nucleic acids; (g) comparative studies of mammalian vs plant enzymes.